1. Field of the Invention
The present invention relates generally to the fields of immunology and protein chemistry. More specifically, the present invention relates to a novel treatment of treatment of neurologic diseases such as amyotrophic lateral sclerosis using compounds such as bathocuproine or derivatives thereof.
2. Description of the Related Art
The discovery of mutations to Cu,Zn superoxide dismutase in a subset of familial ALS cases has raised hopes for understanding the selective vulnerability of motor neurons as well as the pathogenesis of the remaining 98% of ALS cases not related to superoxide dismutase mutations. Neurofilaments give axons their structural integrity and define axonal diameter (Hoffman et al., 1987, Brady, 1993). Neurofilaments are composed of three subunits identified as light (NF-L), medium (NF-M) and heavy (NF-H) which assemble in a 6:2:1 ratio to form long macromolecular filaments (Nixon and Lewis, 1986, Nixon and Shea, 1992). Consequently, NF-L is more abundant than the other two subunits in neurons. NF-L is capable of homologous assembly whereas NF-M and NF-H are not competent to assemble in the absence of NF-L (Cohlberg et al., 1995). Each neurofilament subunit consists of conserved head and rod domains and a more variable acidic tail domain. The rod domains are principally composed of alpha helixes, which wrap around each other to form a superhelix of parallel coiled coils (Lupas, 1996). Neurofilament dimers assemble into protofilaments in a head-to-tail arrangement. The head domain is also important for lateral interactions between neurofilaments (Heins et al., 1993). Two protofilaments wrap around each other to form protofibrils, which in turn combine with three other protofibrils to form the characteristic 10 nm diameter neurofilaments seen by electron microscopy. The assembly of neurofilaments involves many complex associations between subunits, each stabilized by hydrophobic interactions that often involve tyrosine (Heins et al., 1993).
Because axons from human motor neurons extend up to a meter in length and constitute &gt;99% of cell volume, they contain more neurofilaments than other neurons except possibly dorsal root ganglia. The importance of neurofilaments to normal motor neuron viability is underscored by the development of motor neuron disease in transgenic mice expressing point mutations in NF-L or b y overexpressing either NF-L or NF-H (Cote et al., 1993, Xu et al., 1993, Lee et al., 1994). Moreover, axonal transport is disrupted in the NF-H transgenic mice (Collard et al., 1995). Disruption of neurofilament assembly can selectively injure motor neurons, perhaps by interfering with retrograde transport of trophic support from target tissues. Abnormal accumulation of neurofilaments in degenerating motor neurons is one of the pathological hallmarks of ALS, and neurofilaments may be significant targets for superoxide dismutase-catalyzed tyrosine nitration by peroxynitrite (Beckman, 1996 a & b).
Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the selective loss of motor neurons and accompanying loss of voluntary muscular function. ALS typically begins as weakness in one limb during middle adult life and progresses via contiguous groups of motor neurons to ultimately result in paralysis and death within 3-5 years (Williams et al. 1991). Ninety percent of ALS cases are sporadic with no identifiable genetic or environmental risk factors. A familial inheritance pattern has been observed in the remaining 10% of ALS cases and one-fifth of those result from dominant missense mutations to the antioxidant enzyme copper, zinc superoxide dismutase (Cu,Zn superoxide dismutase) (Rosen et al. 1993). Early histopathological changes in ALS include abnormal accumulations of neurofilaments and other cytoskeletal proteins in the cell soma as well as within proximal axonal swellings (Hirano 1991). The clinical course and histopathology of sporadic and familial forms of ALS are similar, providing hope that understanding superoxide dismutase-associated ALS will illuminate the pathogenesis of sporadic ALS.
Over 50 dominant, independently arising mutations at 26 different amino acid positions in the antioxidant enzyme Cu,Zn superoxide dismutase have been described in familial ALS patients (Rosen et al. 1994b; Deng et al. 1993b; Hirano 1991b). All but two of the mutations occur outside the active site and affect amino acid positions important for maintaining the stability of superoxide dismutase. The most common mutation involves an alanine to valine transition at position 4 and is associated with a particularly rapid progression of the disease (Rosen et al. 1994a). Mutant and wild-type enzymes are equally expressed in familial ALS patients and total superoxide dismutase activity may be decreased by as much as 60% in some patients (Bowling et al. 1993). Other superoxide dismutase mutants appear to have near normal catalytic activity (Borchelt et al. 1994). Afflicted individuals express superoxide dismutase mutants from birth in all tissues (Robberecht et al. 1994) even though the pathology in ALS is largely limited to motor neurons. Symptoms of ALS typically do not develop until after age 40, whereupon the disease is largely restricted to motor neurons. Heterozygous mutant superoxide dismutase carriers have a &gt;85% chance of developing the disease (Cudkowicz et al. 1997).
Transgenic mice expressing human ALS-superoxide dismutase mutants suffer motor neuron degeneration, paralysis, and death even though they still express their endogenous wild-type superoxide dismutase (Wong et al. 1995; Dal Canto et al. 1995; Ripps et al. 1995; Gurney et al. 1994). Transgenic mice expressing wild-type human superoxide dismutase do not develop motor neuron disease. Conversely, in Cu,Zn superoxide dismutase-deficient knock-out mice, motor neurons develop normally, though they are more susceptible to cell death after axonal injury (Reaume et al. 1996). Thus, the loss of superoxide scavenging by superoxide dismutase per se cannot account for the selective loss of motor neurons in ALS, though it may play a contributing role. Geneticists ascribe the dominant action of the superoxide dismutase mutants to a gain-of-function. Rather than creating an entirely new toxic function, the gain-of-function may simply be an increased efficiency of an injurious reaction catalyzed by wild-type superoxide dismutase which may also contribute to sporadic ALS.
Superoxide dismutase-catalyzed nitration by peroxynitrite could be one gain-of-function contributing to the development of ALS (Beckman et al. 1993). Peroxynitrite, formed from the diffusion-limited reaction of superoxide with nitric oxide (Padmaja et al. 1993), is an alternate substrate for wild-type superoxide dismutase (Beckman et al. 1992; Ischiropoulos et al. 1992). The reaction of peroxynitrite with superoxide dismutase yields a potent nitrating species that adds a nitro group (--NO.sub.2) to tyrosine residues in other proteins (Beckman et al. 1992; Ischiropoulos et al. 1992). Superoxide dismutase is not inactivated by peroxynitrite and can catalyze nitration indefinitely. In contrast, the formation of hydroxyl radical by the reaction of hydrogen peroxide with superoxide dismutase inactivates superoxide dismutase after only a few catalytic cycles (Wiedau-Pazos et al. 1996; Hodgson et al. 1975; Yim et al. 1996). Although hydrogen peroxide-inactivated superoxide dismutase does not scavenge superoxide or react further with hydrogen peroxide, it is still effective at catalyzing tyrosine nitration (Beckman et al. 1992).
Disruption of neurofilament assembly in transgenic mice lead to motor neuron degeneration (Mathieu et al. 1995; Collard et al. 1995; Cote et al. 1994; Xu et al. 1993). Neurofilaments are important in maintaining the structure and diameter of motor neuron axons. Because axons may constitute as much as 99% of total cell volume, neurofilaments are particularly abundant proteins in motor neurons. Abnormal aggregates of neurofilaments within the cell soma and proximal axons are early pathological events in the development of ALS which may contribute to cell death (Xu, Z. et al. 1993b).
The prior art is deficient in the lack of effective means of treating neurologic diseases such as amyotrophic lateral sclerosis. The present invention fulfills this longstanding need and desire in the art.